One of the many ways to improve engine performance in motor vehicles is by means of electronic controlled valve actuation systems. In these systems, an electronic control unit, ECU, receives signals from several different sensors in the vehicle such as speed, load, temperature, etc., and by means of certain algorithms in the electronic control unit, the optimum time to open and close engine valves is calculated. The optimum time is converted to an electronic signal, either digital or analog, and supplied to a solenoid operated control valve to control the flow of hydraulic fluid or engine oil out of a hydraulic tappet or valve lifter.
U.S. Pat. No. 4,615,306 issued to Russell Wakeman and entitled "Engine Valve Timing Control System" describes a basic engine valve control system wherein the opening and closing of the hydraulic valve lifters creates pressure pulses in the hydraulic fluid to provide a boost pulse to move the lifter to its extreme position. An electronic control unit controls the operation of the solenoid operated valve to add or remove hydraulic fluid from the lifter to create a fluid link in the lifter transferring motion from the timing cam on the camshaft to the engine valve.